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Progress of Geology. a 
madoc slates are thus shown to be indissolubly connected with 
the Llandeilo and other Silurian formations above them; whilst, 
although they also pass down conformably into the zone primor- 
diale, the latter is characterized by the linguloid shells (Lingu- 
lella, Salter) and by the genera Olenus, Paradoxides, and Dike- 
locephalus, which most characterize it in Britain as in other 
regions.* 
I take this opportunity, however, of reiterating the opinion I 
have expressed in my work, “Siluria,” that to whatever extent the 
primordial zone of Barrande be distinguished by peculiar fossils 
In any given tract from the prevalent Lower Aiasiann types, 
there exists no valid ground for differing from Beresinde, de 
Verneuil, Logan, James Hall, and others, by separating this 
rudimentary fauna from that of the great Silurian series of life 
of which stratigraphically it constitutes the conformable base. 
And if in Europe but few genera be yet found which are com- 
mon to this lower zone and the Llandeilo formation (though the 
Agnostus and Orthis are common to it and_all the Silurian 
strata), we may not unreasonably attribute the circumstance 
to the fact, that the primordial zone of no one country con- 
tains more than a very limited number of distinct forms. 
May we not, therefore, infer that in the sequel other fossil 
links, similar to those which are now known to connect the Lower 
and Upper Silurian series—which I myself at one time supposed 
to be sharply separated by their organic remains—will be 
brought to light, and will then zoologically connect the primor- 
dial zone with the overlying strata into which it graduates? Let 
us recollect, that a few years only have elapsed since M. de 
Verneuil was criticised for inserting, in his table of the Palzo- 
zoic Fauna of North America, a number of species as being 
common to the Upper and Lower Silurian. But now the view 
udson River and Clinton formations, or in other words be- 
Llandeilo age. a 
ave thus spoken out upon the fitness of adhering to the clas- 
sifications decided upon by Sir Henry De la Beche and his asso- 
ciates long before I had any relation to the Geological Survey, 
and which places the whole of the Lingula-flags of Wales as the 
* In the last edition of Siluria the distinction was drawn between the lower and 
upper Lingula-flags, but the fauna of the latter is now much enlarged. 
